French Island is a combination generating plant and resource recovery facility. The plant’s two generating units burn wood waste, railroad ties and processed municipal solid waste, called refuse-derived fuel (RDF) – a fluffy, burnable fuel produced on-site at a resource recovery facility built specifically for that purpose. There are also two oil-fired combustion turbines on-site to meet peak generation demands.
Built in the 1940s as a coal-fired generating facility, French Island’s two original units were converted in 1972 to burn oil, a cleaner fuel. However, as oil prices climbed, the units became expensive to operate. In the early 1980s, the company identified a new low-cost fuel in waste wood, and converted Unit 2 to a fluidized bed boiler to burn it. In addition to reducing operating costs, burning wood helped solve a waste disposal problem by using sawdust and wood chips that otherwise would have been buried in a landfill. For similar reasons, the company in 1987 built a facility adjacent to the generating plant to process municipal solid waste into RDF. The necessary fuel handling modifications were made to the plant and Unit 1 also was converted to a fluidized bed boiler, making both units capable of burning a blend of waste wood and RDF. The conversion helped maintain reasonable electric rates for customers, while resolving a solid waste disposal problem for La Crosse County.
The fluidized bed boiler installed at French Island was the first in the United States to be used for commercial power production. The special boiler gets its name because it contains a bed of sand that behaves like a boiling pot when air is injected into it. As the RDF or waste wood fuel is fed into the boiler, it mixes with the sand and remains suspended in the air – being constantly scraped to reveal fresh combustion surfaces. Unlike conventional boilers, the fuel used in a fluidized bed boiler does not have to be uniform in size and moisture content to burn thoroughly.
French Island’s resource recovery facility has the capacity to process more than 100,000 tons of municipal solid waste each year. The RDF processing facility removes non-combustible materials from the waste, then chops and shreds it into a uniformly sized fluffy product that is burned with waste wood and railroad ties.
Waste wood, railroad ties and RDF contain low levels of sulfur, so sulfur dioxide emissions are minimal. The duct scrubbing system uses dry lime injection to help further decrease emissions of sulfur dioxide and hydrogen chloride. Improvements also have been made to the combustion process inside the fluidized boiler to help control emissions. Pulse jet bag houses efficiently collect particulate matter, including mercury and dioxin and metals such as lead and cadmium, in order to minimize their release to the air. A urea-injection system on both boilers helps reduce emissions of nitrogen oxides.
French Island is an integral part of the La Crosse County Solid waste program. To date, we have kept 1.32 million tons of waste out of the La Crosse County landfill, avoiding 5 medium sized landfills.
The county and the plant have partnered on ferrous and non-ferrous recycling. The plant recycles nearly 1000 tons of ferrous and 250 tons of non-ferrous annually.
Plant employees conduct tours for 900 people annually, including local clubs, schools, professional organizations, engineering firms, environmental students, county employees, and elected officials.
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